It is generally known that thermosetting compositions are prepared from compounds having carboxyl groups and compounds having reactive functional groups which can form chemical bonds with the carboxyl groups by heating, such as epoxy group, oxazoline group, silanol group, alkoxysilane group, hydroxyl group, amino group, imino group, isocyanate group, blocked isocyanate group, cyclocarobonate group, vinyl ether group, vinyl thioether group, aminomethylol group, alkylated aminomethylol group, acetal group and ketal group.
As the thermosetting compositions described above, for example, compositions comprising combination of carboxyl groups and epoxy groups have been disclosed in Laid Open Japanese Patent Application Showa 51-114429, Laid Open European Patent Application 29595 and U.S. Pat. Nos. 4,371,667, 4,650,718, 4,681,811, 4,703,101 and 4,764,430.
The compositions comprising combination of carboxyl groups and oxazoline groups have been disclosed in U.S. Pat. No. 3,505,297 and Laid Open Japanese Patent Applications Showa 60-88038 and Heisei 2-115238.
The thermosetting compositions give cured products having excellent chemical properties, physical properties and weathering resistance and are widely utilized in the field of coatings, ink, adhesives and molded articles.
However, the reactivity between the carboxyl group and the reactive functional groups is high so that compositions in which compounds having carboxyl groups and compounds having the reactive functional groups exist together have problems that the compositions are gelled during storage and the period suitable for pot life is short.
The compounds comprising carboxyl groups conventionally utilized for thermosetting compositions described above have problems that solubility to generally used organic solvents is low and that compatibility to the compounds having reactive groups, which react with the carboxyl group, is inferior because of the property of the carboxyl group capable of forming strong hydrogen bonds. When the thermosetting compositions are utilized as top coating compositions, there are naturally have problems that preparation of coating composition of high solid content is difficult and that appearance of the finished coat is inferior.
For the purpose of solving these problems, it was proposed that carboxyl group was blocked by converting it to tertiary-butyl ester and the ester was decomposed by heating, and the free carboxyl group was regenerated by elimination of isobutene (Laid Open Japanese Patent Application Heisei 1-104646).
However, this method is not sufficiently satisfactory in view of resource saving and energy saving because of the requirement of a high temperature, such as 170-200.degree. C., for the heat decomposition of the tertiary-butyl ester. And also, this method is not sufficiently satisfactory because of the problem that pock marks which were made by foaming and degassing of isobutene formed by the decomposition remained on the cured surface of the coating.
In recent years, many oil droplets and dusts have existed in air by environmental changes such as air pollution. As the result, some problems have occurred, among which paint film on buildings, automobiles and the like are easier to be stained than former and it's stain is difficult to remove. Thus, it has been desired that paint films have resistance to the stain, i.e. stain resistance and property to remove stain from stained paint films, i.e. stain-removing property. In such circumstances, it is desired to produce coating compositions which give paint films having excellent stain resistance, stain-removing property, weathering resistance, light resistance, gloss, appearance, water resistance and chemical resistance and is excellent in environment protection property and safety property.
Convenient leading coating compositions having stain resistance, which have been used, comprise a fluorine-containing resin as a main component. The stain resistance of the coating compositions is attributed to excellent weathering resistance and water repellency of the fluorine-containing resin, as explained the following. The fluorine-containing resin manifest the performance by (1) light, heat and chemical stabilities caused by larger bond energy between fluorine atom and carbon atom compared with that between hydrogen atom and carbon atom and (2) water repellency and oil repellency caused by larger atomic radius of fluorine atom compared with that of hydrogen atom and lower surface free energy attributed to lower polarizability between fluorine atoms (0.68.times.10.sup.-24 cc).
In order to increase solubility to a solvent in using the fluorine-containing resin for a coating composition, a copolymer of a fluoro olefin and a vinyl ether monomer such as cyclohexyl vinyl ether (described in Laid Open Japanese Patent Applications Showa 57-34107) and a resin mixture of a fluorine-containing resin and an acrylic copolymer (described in Laid Open Japanese Patent Applications Showa 61-12760) were known. But, these do not manifest sufficiently the excellent weathering resistance and the stain resistance characteristic of the fluorine-containing resin because of the small amount of the portion based on fluorine-containing monomers.
Also, in order to improve the weathering resistance and the stain resistance of the fluorine-containing resin for a coating composition, a copolymer of a fluoro olefin, a .beta.-methyl substituted-.alpha.-olefin, a monomer having a chemical curing reactive group and a monomer having an ester group in a side chain was proposed (Laid Open Japanese Patent Applications Heisei 4-279612). But, the satin-removing resistance is not still sufficient.
On the other hand, a coating composition, which gives weathering resistance with an acrylic polyol produced by reacting a polymerizable monomer having stability to ultraviolet rays as essential component, is near recently suggested as a coating composition having excellent weathering resistance (Laid Open Japanese Patent Application Publication Heisei 1-261409). But, there is no description about stain resistance in this publication.
A coating composition comprising a partially condensate of an organic silicon compound and a specific silica praticulate was suggested as a composition having stain resistance (Laid Open Japanese Patent Applications Heisei 2-3468). But, there is no detailed description about a resin ingredient used in the coating composition in the publication.
The inventors have already suggested a thermosetting composition comprising a compound having functional groups in which carboxyl groups are blocked with vinyl ethers, and a compound having reactive functional groups which react the functional groups (Laid Open European Patent Application 643112) in order to solve the problems described above. But, a thermosetting composition which gives paint film having further excellent stain resistance, stain-removing property and moisture resistance is needed in some uses.
Thus, a coating composition, which gives paint films having stain resistance, stain-removing property, weathering resistance and light resistance, has been not developed.
The present invention accordingly has an object to provide thermosetting compositions which give cured products having weathering resistance, chemical properties, physical properties, particularly stain resistance and stain-removing property at lower temperatures and have excellent storage stability, and can be utilized as high solid one component coating materials.
Another object of the invention is to provide methods of coating which discharge a small amount of organic solvents into air during coating and give excellent appearance to the finished articles and to provide articles prepared by utilizing the methods of coating.
Extensive investigations undertaken by the present inventors with the objects described above lead to a discovery that the objects can be achieved by a composition comprising: (A) a compound having in the molecule two or more carboxyl groups which are blocked by a specific vinyl ether group, vinyl thioether group or heterocyclic group having vinyl type double bond and oxygen or sulfur as the hetero atom component; (B) a compound having in the molecule two or more reactive functional groups which can form chemical bonds with the blocked carboxyl groups by heating, and (C) a dispersing component of at least one inorganic oxide sol selected from the group consisting of an aluminum oxide sol, a silica sol, a zirconium oxide sol and an antimony oxide sol; and optionally (D) a thermal latent acid catalyst which is activated during curing the composition by heating; or by a composition comprising: (E) a self-crosslinkable compound having in the molecule one or more blocked carboxyl groups and one or more reactive functional groups which can form chemical bonds with the blocked carboxyl groups by heating, and ingredient (C) and optionally, ingredient (A) and/or ingredient (B), and further optionally ingredient (D).